Great insulation both ways. I have been using older…

I have been using older sizes of the very same flask for ages now. Each and everyone of them fulfilled my expectations just fine. The last addition to my Stanley line of steel flasks is this 16 oz one. The same old great product gets even smaller, which is just the perfect size for a winter backpack.

The whole thing inside and out is steel, so I do not worry about the hot water coming in contact with a plastic material. However, the inner cap and the inside of the screw on drinking cup are plastic, which I hope is BPA free.

Anyhow, I am using it while attempting a mountain climb during winter time. It holds a decent 16 oz of liquid amazingly hot for I do not know how many hours; 12 hours guaranteed, 14 to 16 hours relatively hot. I am pre-warming the inside first, then filling it with boiling water.

The cap screws down fine, closing with two siliconized gaskets so you do not worry about any leakage inside the pack. The lid, a.k.a drinking cup, is 8 oz ,which is what the manufacturer states. It holds the perfect amount of water if the activity will last 12 hours or so, if it will last longer you can always refill it.